add read/write optional text

src/main/java/org/elasticsearch/common/io/stream/StreamInput.java

@@ -192,6 +192,15 @@ public abstract class StreamInput extends InputStream {
         return null;
     }
 
+    @Nullable
+    public Text readOptionalText() throws IOException {
+        int length = readInt();
+        if (length == -1) {
+            return null;
+        }
+        return new StringAndBytesText(readBytesReference(length));
+    }
+
     public Text readText() throws IOException {
         // use StringAndBytes so we can cache the string if its ever converted to it
         int length = readInt();

src/main/java/org/elasticsearch/common/io/stream/StreamOutput.java

@@ -184,6 +184,14 @@ public abstract class StreamOutput extends OutputStream {
         }
     }
 
+    public void writeOptionalText(@Nullable Text text) throws IOException {
+        if (text == null) {
+            writeInt(-1);
+        } else {
+            writeText(text);
+        }
+    }
+
     public void writeText(Text text) throws IOException {
         if (!text.hasBytes() && seekPositionSupported()) {
             long pos1 = position();